• Linus Torvalds's avatar
    Revert "tty: make receive_buf() return the amout of bytes received" · 55db4c64
    Linus Torvalds authored
    This reverts commit b1c43f82.
    
    It was broken in so many ways, and results in random odd pty issues.
    
    It re-introduced the buggy schedule_work() in flush_to_ldisc() that can
    cause endless work-loops (see commit a5660b41: "tty: fix endless
    work loop when the buffer fills up").
    
    It also used an "unsigned int" return value fo the ->receive_buf()
    function, but then made multiple functions return a negative error code,
    and didn't actually check for the error in the caller.
    
    And it didn't actually work at all.  BenH bisected down odd tty behavior
    to it:
      "It looks like the patch is causing some major malfunctions of the X
       server for me, possibly related to PTYs.  For example, cat'ing a
       large file in a gnome terminal hangs the kernel for -minutes- in a
       loop of what looks like flush_to_ldisc/workqueue code, (some ftrace
       data in the quoted bits further down).
    
       ...
    
       Some more data: It -looks- like what happens is that the
       flush_to_ldisc work queue entry constantly re-queues itself (because
       the PTY is full ?) and the workqueue thread will basically loop
       forver calling it without ever scheduling, thus starving the consumer
       process that could have emptied the PTY."
    
    which is pretty much exactly the problem we fixed in a5660b41
    
    .
    
    Milton Miller pointed out the 'unsigned int' issue.
    Reported-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    Reported-by: default avatarMilton Miller <miltonm@bga.com>
    Cc: Stefan Bigler <stefan.bigler@keymile.com>
    Cc: Toby Gray <toby.gray@realvnc.com>
    Cc: Felipe Balbi <balbi@ti.com>
    Cc: Greg Kroah-Hartman <gregkh@suse.de>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    55db4c64
tty_ldisc.h 5.87 KB